Measures of psychological similarity or proximity, and scaling methods for their analysis, provide a means of understanding the psychological organization of perceptual and cognitive domains. The proposal describes a model that assumes measures of interobject similarity are a joint function of continuous variation along implicit stimulus dimensions and hierarchical ordering on the objects. The continuous variation is represented spatially as in multidimensional scaling. The hierarchical ordering is represented by a degenerate tree structure that specifies the varying degrees of association between the individual stimuli and superordinate level descriptor(s). The proposal outlines a number of experiments designed to provide an empirical basis for the development of the model. The approach uses multiple tasks to measure interobject proximity and the hierarchical ordering imposed by the superordinate. An application of the model to data on musical pitch structure is given, and further experiments are described that investigate the representation of multiple, ambiguous, and changing tonal organizations. The second group of studies applies the model to the domain of rhythm in which the continuous dimension is the time dimension itself, and the hierarchical component is the hierarchy of rhythmic stress imposed by the context. The experiments measure both the hierarchical ordering and inter-event proximity, and consider the perception of changing and multiple rhythmic organizations. The third group of studies is concerned with the applicability of the model to visual forms and conceptual categories. THe model to be developed and tested by these experiments is sufficiently general to describe both within-level and across-level psychological relationships, and may account for various task and context effects noted in the scaling literature. The experiments, in addition, consider common structural features of internal representation that cut across a wide variety of cognitive and perceptual domains.